Metal foil honeycomb core



Sept. 2, 1952 T. P. PAJAK 2,609,068

METAL FOIL HONEYCOMB CORE Filed March 11, 1949 m ww Patented Sept. 2, 1952 METAL i on. HONEYCOMB com:

. Theodore P. Pajak, Baltimore, Md.', a'ssignor to The GlennL. Martin Company, Middle. River, Md., a corporation of Maryland Application March 11, 1949, Serial No. 80,955

This invention relates to an ir'n'proved'structural material and, more particularly, to a material having a 'metal honeycomb core formed with indented and apertured cell walls including the method of making such material.

In the forming of a metallic cellular panel, in which surface sheets are placed transversely of cells formed from sheet material bonded together and. to the sheets by an adhesive under heat and pressure the necessity of dissipating the vapors liberated by the bonding adhesive becomes a serious problem. Such vapors, if not readily dissipated, have a tendency to form bubbles that detract from the strength of the bond formed by the adhesive and create internal pressures sufficient to blister thesurfacesheets. These problems have been solved inthe construction of the panel structure of this invention in which strips of foil are perforated to form ventilating means positioned and arranged for the dissipation of vapors liberated by the adhesive. The perforated metal foil strips of this invention are corrugated to provide flat surfacesdisposed on each side of a medianplane, which are then assembled together to iorm a unitary structure having a plurality of cells adhesivelybonded together between surface sheets with the ends of the cells joined to the inner, sides of the sheets. The perforations of 19 Claims. (01. lit- 34) f a of gases and vapors bonded together at said areas the strips provide air passages leading from each bond area for the ready transmissionof vapors from cell to cell and outwardly of the structure. Such ready transmission of the vapors as the adhesive isheated overcomes their tendency to form air bubbles in the'bond areas and allows the vapors to pass out of the cells under selfgenerated pressureswithout aifecting the structural arrangement of the cells or surface sheets.

. The present invention provides a structural ma terial having a light-weight core formed of indented and apertured metal foil strips corrugated andbonded together as a plurality of vented cells positioned between face sheets. The are rangement of the apertures of the metal foil strips assures the'formationiof complete uniform bonds throughout each bond area free of air bubbles and the liberationof solvents and polymerization products during the bonding operation. The arrangement of the indentations and. apertures of this invention alsoallo'ws for the uniform distortion of the cell edges of an assemblage used tion. to provide a cellularstructural material 5o to produce a'structure having curved panel areas wherein certain areas ofthe cell walls are'caused tobecome disarranged as the cellular material isgformedto the configuration of. the innersur comprisedof strips. of metal: foil having inter 'veninglb'o'nd areas 'aperture'd for; the dissipation to form a plurality of cells in a cellular assembly placed between surface sheets andbonded thereto. l

Another object is to provide a structural ma terial having surface sheets separated by a cellu-- lar 'core formed of apertured metalstrips bonded together at spaced intervals.

Still another object is toprovide a structural material having a metal cellular core formed of metal foil strips formed with surface irregularities wherein the rigidity of each strip is increased.

Another object is to provide a structural material having an assembly of vented cells formed of reinforced metal foil strips bonded together I and between surface sheets formed of material having substantially the same'coeflicient of expansion as the cellular material.

A further object is to provide a rigid structural versely. thereto and bondedto the endsl ofsaid cells. 7

Another object of this invention is to prpvi d et a method of forming reinforced, cellular; metallic f structural material having a specific gravity of from .016 to .18.

Other objects of this invention will become;

apparent from the following description when taken in conjunction with the accompanying drawing in which like numbers refer to like parts in different views. K p

In the drawing: l

Figure 1 is a perspective view of a sectionjofi the cellularstructure of ,this invention. I

Figure 2 is a fragmentary perspective viewbff the core construction showing the ventedand; indented formation of the foil strips, 1 f .Figure 3 isa perspective view of a sectiongof f the cellular structure having. curved surface" sheetsfshowing the folded formations developed;

in the cell walls.

' Referring more specifically tothe drawinglin j" Figure l, I have illustrateda section ofthe' cellu lar structure of this invention constructed as a flat panel for use as a flooringmaterial ore.

like application where'a fiat panel would be suitable. The panel" Ill consists of 'a' top sheet" II and a bottom sheet l2 "of aluminum alloy on like material'held separatedby' a. cellular core-t in which a plurality of hexagonal cells; .I 31.:arej;

each cell l3 are'bonded to the inner surfaces of the top and bottomish'eets ll and i2 'respectitielxiiij; placed transversely thereto.

Uniformly spaced transversely and longitudi- 5 nally of each of the strips H are indentations 23L formed as deformations in the strip. ,surface.;, The function of these indentations is to add rigidity imately twenty minutes at substantially 300 F.

with the assembly of strips held together under suiiicient; *pressuregto provide 'a close, upcture betweenthe strips at the bond-area 'as' best shown in Figure 2. The core material so formed as an assembly of cells [3 extending between the bonded strips .11 is then ready for further processing.

The desired thickness of core material for use to the strips I! which not onlyaidssin .workingse zbetweenzzmetal; surface; sheets H and I2 is cut the material but also increases v the strength-of the finished structure. The need for additional-;-- rigidity of the strips l1 dependssgreatlymnjhe application and whether or not a heat "treated" or a non-treated foil is to be used. I have found 7 that fully hardened aluminum foilof from .001.

30152006 ffi i'iani inchcinathickness;,un iqrm epp rugatedm indented; with*de prmatione' evine; pthmfzf-mm?aofifi tcsfi tsofsaminch;s ace-Ga proximately .100 of an inch apart, provides a foll strip: Urinating: s p charmterist es t 1,. v

clesiliic zapnnoxim el I a-9i an my etc-r ioman rsqximate az /i bestiil ust lated ellularv wmt iamr In l'h tli ali pg mhe. c rru ated ;-a dfiinterv ning area so s to facilitate-ths-mh orm.ld sSi ation of. yapors'fand i gas esjoriginatingf 1hinfvthe coreyduring ;the .j moldin andgbondi qpera on l j .Iil .the-Ibrmingpflth core material' the outside;

surraegor, egcn riagey, ma mas be jo ined 9 4 gether by bonding is'co'vered with a. fairly heavy coat .oi; thermosettingmdhesive suitable. for b6 Itlis t ibe-unde'r'stood,

m o bo din uch s. solder n' lbra r me or. we1ding;,,,howeiler, ny method, thatwould t ncy 'toyincrease the.wei htgshouldg.

by preheating only sufii'ciently to flxjtheadhesive in ,,a, rebcnded stat -It .w s f mer y considered sarythat .hi ep e iminate .a lii i h'e sidualsolventr mi leadhesive" niv ewofith fact xatiescaneg th s i nt .durinethQIinaL bbfidi woulgipr ..imp c a1 'lfhea ertur df inven i n al ows .fe without 'jpresentin'gh ofi'n' the present invention to attain a lhighgr fg'65"thdiif speed.Conforming; In. the .present. meth dgof a si to fiicierr 31. b reo ri sy t rf m the-des red: idth arezistackedu mp ted bv he apnlic'ation oflheatafor approx-#75 eriorl tr u haandsrieiditv eo o co e:,- o' e ch ofl .su ia w n h;se ter se ms: ac ual=; n ee the .730: ;ar e bonded-to. thelcellu1ar,.core

"l'henekt 'step isto'partially cure-the adhesive "curvedj,su1jf ace.' This forfrjati from.-.thelassembly..of strips by sawing or sanding *by meansofsany of the conventional tools common;,to woodworking. Inasmuch as most of the structural'material presently formed from .coretmaterial of this type is approximately of an inch in thicknessrit apparent that an as-' mblyeoij anp prov des. r l

he.-ifi a .i;a .emb Phe next step i iae i i t k .anuteetu i ai u. and fl with jecting thejassembly} shown; I andpressi'ire i i a conventiorialetypefjof oven Nolspeciallprovisi'ohneedbe mad fo liberation bfthe vaporsereatd while material as these Lvap'ors are' .ijeadil I: H outwardlypf thetcorelmaterialjthroug jpe u I6, unifiormly 'pl'aedjtlrMu'gliQiit,the material n bssae tunesilfi s arr need o asta r y ven v n e c @495 I hav el a appl ma th lt i t an g t be deformed to fo1low:

terial, ;jt.o-. nform with I1n iuifi curved. face. sheet .1 Bastien as tnefconve c irv u v i .b itp s'h'eet 'lbr i ea i d .u qio t e rmali y. p 'l 1 b'o'ndedf together fas previouslyjdescrlibe and shaped tio thesame curvatures as the" sheets:- 'I walls"offthe eellsfl3 are merely, fold "baa" i eeqtont insidesurfae f thefbdttoni she I a r 'radrb'et'weem heftwd su f" withthe-met 'i t""lgiii thd'sired suchfaformationith top pripheryiof ach" ell remains substantially{the sam a'nd -th otto'm; periphery-is red'uced dueto thfieonipressi' or'cei- 70 pplied to th celrwalis next-41o the bottomisheetia 20. The tendency f'of "the foil 'to --Icrinkle1l iinto":a wrinkles ilji'extending 1ateral-ly "of thetcell mus y taken a'dvanta'gfofi to prbdueegth deaf:

siredstructure? The endeio'fitheme'll wallaplacaic adjecent th'ebdttoni sheet llkar'eatlso iolddgovee'r as reentrant areas 22 which adds to the bond areas attainable between the curved bottom sheet 20 and the adjacent ends of the cell walls.

While I have illustrated and described with particularity the forming of a panel structure according to my invention, it will be appreciated that certain changes, alterations, modifications and substitutions can be made without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A cellular structural material comprising a pair of metal surface sheets separated by a cellular core formed of aluminum foil strips bonded together at spaced intervals with intervening spaces separated to form a plurality of cells, said strips being formed with a plurality of apertures extending therethrough for liberating vapors and gases from within each said cell with the ends of said cells being adhesively joined to the surface sheets by a thermosetting resin to form a vented unitary structure.

2. A cellular structural material comprising metal surface sheets separated by and adhesively bonded by a thermosetting resin to a cellular core formed of a plurality of metal foil strips arranged cdgewise between said sheets and each having bond areas displaced from a median plane with intervening areas separated so as to form hexagonal cells, said strips being formed with apertures arranged as air passages leading from each said cell for the passage of gases liberated at said bond areas during the bonding of the material under heat and pressure.

3. A cellular structural material comprising metal surface sheets separated by and adhesively bonded under heat and pressure to a cellular core structure, said core being formed with a plurality of perforated aluminum foil strips each being corrugated to form bond areas displaced on each side of a median plane with the intervening areas of said strips forming hexagonal cells, said perforations in the strips venting each said cell so as to provide for liberation of gases and vapors formed by the adhesive during the bonding operation.

4. A cellular structural material comprising a cellular core of metal foil strips formed with a plurality of surface indentations spaced longitudinally and transversely of said strips as a stiffening means and adhesively bonded together at spaced areas displaced from the median plane of each strip to form hexagonal cells, vent means for each cell and bond area comprised of apertures formed in each strip forming air passages leading from the cells with the ends of said cells bonded to the inner surfaces of face sheets to form a unitary structure.

5. A cellular core for use in a structural panel having face sheets separated by a core comprising a plurality of aluminum foil strips having spaced perforations extending therethrough as vent means, said strips being formed with transverse ridges placed back to back to form a plurality of cells having ends adapted for bonding to the inner surfaces of the face sheets placed thereacross.

6. A cellular construction comprising a plurality of metal foil strips formed with bond areas spaced between intervening areas and displaced from the median plane of each strip and bonded together by a, thermosetting adhesive to form a plurality of cells, vent means for said bond areas consisting of apertures formed in the strips at the bond areas and the intervening areas positioned and arranged to form air passages leading outwardly of the cells for the liberation of gases and vapors formed at said bond areas.

7. A method of constructing a structural comprising the steps of indenting a strip of metal foil to add rigidity thereto, perforating said strip with vent holes for the passage of gases therethrolugh,

corrugating said foil transversely to form alternately raised and depressed areas displaced from the median plane of the strip to provide ridgelike bond areas spaced at each side of the median plane of each strip, cutting the formed strip into sections, coating said bond areas with an adhesive, positioning the strips with the coated bond areas together with the depressed areas spaced opposite each other to form hexagonal cells, bonding said cells together to form a core unit, coating one side of each of a pair of metal surface sheets adapted for engagement with the ends of said cells of the core unit with an adhesive, positioning the coated areas of the surface sheets across the cell ends and bonding the core unit and surface sheets together as a unitary structure with the gases liberated by the adhesive being vented through said vent holes to the exterior of the structure.

8. A method of constructing a structural panel comprising the steps of perforating said strip with vent holes for the passage of gases therethrough, corrugating said foil transversely to form alternately raised and depressed areas displaced from the median plane of the strip to provide ridge-like bond areas spaced at each side of the median plane of each strip, cutting the formed strip into sections, coating said bond areas with an adhesive, positioning the strips with the coated bond areas together with the depressed areas spaced opposite each other to form hexagonal cells, bonding said cells together to form a core unit, coating one side each of a pair of metal surface sheets adapted for engagement with the ends of said cells of the core unit with an adhesive, positioning the coated areas of the surface sheets across the cell ends bonding the core unit and surface sheets together as a unitary structure with the gases liberated by the adhesive being vented through said vent holes to the exterior of the structure.

9. A sandwich panel structure comprising a pair of reinforcing sheets and a plurality of perforated aluminum foil strips interposed edgewise therebetween, said strips being corrugated so as to provide abutting crests extending generally normal to the plane of said sheets whereby to form a cellular core, said strips being bonded to their adjacent strips at said abutting crests and to said sheets with a thermosetting adhesive to form a unitary structure, said perforations in said strips venting each cell whereby to permit the escape of gases generated by said adhesive.

THEODORE P. PAJAK.

REFERENCES. CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,389,294: Dean Aug. 30, 1921 1,754,784 Borsodi Apr. 15, 1930 1,996,490 Romanoif Apr. 2, 1935 2,050,074 Trytten Aug. 4, 1936 2,056,563 Budd et al Oct. 6, 1936 2,385,352 Davis Sept. 25, 1945 2,428,979 May Oct. 14, 1947 2,477,852 Bacon Aug. 2, 1949 2,512,875 Reynolds 'June 27, 1950 

